Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: "B. Pym" <Nobody447095@here-nor-there.org>
Newsgroups: comp.lang.lisp
Subject: Re: which articles are sold?
Date: Mon, 23 Jun 2025 08:53:21 -0000 (UTC)
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Lieven Marchand wrote:

> > if we have this list:
> > (a <sold> b c d <sold> e f g <sold>)
> > that shows that article a, d and g are sold and the rest are not how
> > can we put all the sold articles in one list:
> > (a d g)
> 
> More homework?
> 
> (loop for (first next) on '(a <sold> b c d <sold> e f g <sold>)
>       when (eql next '<sold>)
>       collect first)

Scheme:

(define items '(a <sold> b c d <sold> e f g <sold> h i <sold>))

(filter-map
  (lambda(x y) (and (eq? '<sold> y) x))
  items
  (cdr items))

 ===>
(a d g i)